Conventional shutoff valves, such as emergency shutoff valves, may be inserted in the side of a storage tank containing a material, such as a liquid, or in the piping used to direct the flow of the material. Shutoff valves may be used to control the flow of material from, or to, the tank, or the flow of material within the piping.
Conventional valves are actuated by hydraulic pressure, which pushes a main piston away from an opening to open the valve. Removing the hydraulic pressure causes the valve to close by the action of a single spring acting on the main piston, thereby preventing unwanted flow of material from the tank, or through the pipe. Conventionally, the valve is controlled by one or more fuse plugs. In an emergency, such as a fire, one or more of the fuse plugs in the actuating line melts, and causes a release of hydraulic pressure, and the shutting of the valve.
Conventional shutoff valves typically rely on an external hydraulic pressure meter to determine if the valve is open or closed. However, conventional shutoff valves may suffer because the hydraulic pressure meter is not always installed, and thus, the hydraulic pressure, and valve position cannot be readily determined; the hydraulic pressure meter is prone to be inaccurate; and/or the meter does not work. In addition, an operator cannot really determine the true position of the piston in the valve. For example, the piston may become stuck or otherwise immobilized, such as by the failure of the one spring acting on the main piston, and the hydraulic meter may still reflect a decrease in hydraulic pressure in the line, but would not be able to indicate that the piston in the valve is stuck.
Thus, there remains a need for an improved shutoff valve that provides a reliable indication of the shutoff valve position.